hv      Mountain medicine link


Altitude Illnesses

Only in the last 100 years has it been recognized that insufficient of oxygen at altitude was the cause of a number of medical disorders that occurred to travelers and people living at high altitude.

The percentage of oxygen in air is always 20% but at higher altitude air is more rarefied, under less pressure so that less oxygen is available.

People and animals have adapted to high altitudes but travelers are more susceptible as they have to undergo acclimatization to become adapted to the new environment.

We have described below some of the more common problems that are associated with altitude, how they may be prevented, their early recognition, and methods on how they may be treated.

Despite the easy categorization of symptoms into convenient syndromes there is still much to be learned about altitude.

We have included links to societies and websites that our visitors may go to to learn more.

The definition of altitudes have been broken into 3 broad levels:

Altitude or "Moderate altitude"8,000-12,000 feet (2400-3600 meters)

About 25% of those traveling to 2400m may experience mild mountain sickness. At 2700-3600m about 40% of people may have symptoms. More severe altitude diseases do occur but are less common. People going to recreational ski or climbing activities would be exposed to this type of altitude.

High Altitude (12,000-18,000 ft or 3600-5500m)
This altitude may be reached by climbers in North America, base camps on Mountaineering expeditions and trekkers. Usually mountaineers are very aware of the perils of altitude but recreational trekkers that travel without specialized equipment may still be at significant risk but without awareness of their danger.

Very High Altitude (18,000-29,000ft or 5,500-8,800 m)

These areas are usually only visited by well equipped expeditions. Humans live permanently at altitudes of 17,500 (5400m) but above this they do not thrive. Above 20,000 ft (6100m) people deteriorate rapidly (extreme altitude)


Acclimatization is the process where a person makes adjustments to continue to oxygenate themselves. It can also be viewed as a series of adaptatations by an organism to optimize delivery of oxygen to the mitochondria inside the cell.

In diseased individuals these processes may be impaired and they are more likely to have failures to acclimate adequately. Increased rate and depth of breathing occurs first.
Carbon dioxide is exhaled more and this causes the pH of the blood and cerebrospinal fluids to be higher (or more alkaline) or what is called a respiratory alkalosis.

This stimulates the kidneys to excrete bicarbonate to attempt to restore the normal pH (compensatory metabolic acidosis).
Acclimatization varies between individuals.

If a person is slowly exposed to altitude they will have little difficulty but because of instantaneous travel many travelers may not have the opportunity to be properly prepared.
General advice to recreational vacationers at 8-10,000 ft is that they should not exercise vigorously for 1-2 days after arrival. But this is clearly what ski vacationers do not do.

For climbers it has been suggested to take one day to climb each 1000ft above 10,000ft. But this is conservative and may not apply to everyone. Above 12,000ft people should go at their own pace. If going with a group excursion it is important to go with buddies who will wait and not rush the members who are acclimating poorly.

Acute Mountain Sickness

AMS is the most common altitude problem and is caused by changes in the circulation of the brain. Mild or moderate symptoms include headache,and sometimes nausea. The headache is usually throbbing in the back of the head and is worse in the morning after awakening.

Other symptoms include dizziness, fatigue, anorexia, poor sleep and malaise.

The symptoms usually start 12-24 hrs after onset and improve by 72 hrs.

Poor balance (ataxia) is found in severe AMS.
Children including preverbal infants have been recognized to suffer at least as often as adults (see later section)
Older individuals may be less susceptible since a slightly atrophic brain size may accommodate mild cerebral edema easier.

Anyone who has had a rapid ascent with the above symptoms should be considered to have AMS.

If their condition is worse despite rest they should be given oxygen and they should descend.

They should avoid heavy exertion, alcohol and nicotine.

Extra fluids and high carbohydrate diets are helpful.
Tylenol and aspirin can be taken for headaches.

Acetazolamide (diamox) is used to prevent altitude illness. It speeds acclimation and does not mask symptoms. It acts by excreting bicarbonate. The suggested dose is 125mg twice daily starting one day before and continuing 2-5 days after arrival. In children this dose is 5mg/kg/day Diamox works better in preventing altitude disease than treating it.

High Altitude Cerebral Edema (HACE)
Usually at altitudes above 12,000 ft people with AMS may develop more severe symptoms of ataxia, confusion, hallucinations, poor memory and impaired judgement.

Progression may occur to coma and death.

Anyone suspected of HACE should be given oxygen and evacuated to a lower level and must be accompanied during their descent.

Descent of a few thousand feet may bring dramatic improvement.

Dexamethasone ( a steroid medication ) is given for HACE but should be used under medical supervision. Hyberbaric bags such as the Gamcow bag are occasionally available but are no substitute for descent but may buy time in extreme cases.

High Altitude Pulmonary Edema
HAPE is another condition that may or may not be associated with AMS, and is sometimes coexistant with HACE.

At above 12,000 ft 1-2 % of people have HAPE.

Pulmonary edema develop and unless promptly treated individuals may become comatose and die. Symptoms usually begin 2-4 days after arrival and typically on the second night Early signs are dry cough, increased heart rate, decreased exercise tolerance, shortness of breath with exercise, and increased recovery time from exercise.

Also a tightness in the chest at night is noted.
Later the cough becomes productive at first white then blood tinged, high heart rate and breathing, cyanosis and wheezes.
Usually the person will be profoundly more tired than others.
HAPE may affect anyone, even people who are seasoned mountaineers.

The most important treatment is descending.
If they cannot walk they must be carried and kept warm with oxygen.
Nifedipine oral 10mg at once and 20-30 extended release may help.
Diamox 125 mg twice daily may help for those with poor ventilations.
Viagra (sildenafil) is being studied as both a preventative and treatment drug for HAPE.
Diuretics such as lasix (furosemide) should not be used.

Prevention of HAPE
Acetazolamide The suggested dose is 125mg twice daily starting one day before and continuing 2-5 days after arrival. In children this dose is 5mg/kg/day
Nifedipine 20mg every 8 hrs for those known to be susceptible to HAPE (Pulmonary Hypertension , single pulmonary artery)

Summary of Altitude Prevention

Travelers are always recommended to take slow ascents.

Climb high and sleep low.

Trying not to sleep greater than 2000ft higher than the previous night is helpful.

For prolonged trips an extra day of acclimation for every 3,000 ft gained is also a good idea.

A high carbohydrate diet >70% improves respiration and this may reduce altitude illness by 30%.

Respiratory depressants- alcohol and sleeping pills should be avoided Chemprophylaxis or drugs to prevent illness may be considered: Diamox 125mg twice per day or 5mg/kg/day in 2-3 divided doses.

Dexamethasone ( a steroid) 4mg every 6-12 hrs is sometimes used but must be given with extreme caution. This drug does not speed acclimatization and if it wears off while at altitude travelers are at extreme risk of problems.


Other Altitude problems:

High Altitude Retinal Hemorrhage (more common above 12,000ft)

These small bleeds in the retina may result in blurry vision or small areas of blindness.

This is painless and only seen with an opthalmoscope.

These will resolve with no treatment even at altitude although large bleeds should descend and wait for resolution.

People with radial keratomy corrective eye surgery also run into visual problems and should descend if problems.

This is different from retinal haemorrhages.

The newer Lasix corrective eye surgery is safe for travelers to altitude.

High Altitude Systemic Edema
This condition causes swelling to the feet and hands; and also the face and eyelids in the morning. It is harmless and usually clears up. Restricting salt and drinking extra fluids will help resolve it. Diamox through its diuretic effect also improves it.

Weight loss at altitude

Some climbers will lose weight at altitude. Appetites may be poor so food should be selected that is desirable. Carbohydrate rich foods are better tolerated than fatty foods.

Extreme Altitude Deterioration

People may live normal lives at altitudes up to 17,500 ft and may work for several weeks at 20,000 ft but at higher levels deterioration instead of acclimatization occurs. Cold , hypoxia, and exhaustion may all play a part.

Chronic Mountain Sickness

Occurs in residents at altitudes of 15,000-17,000 develop an abnormally high haemoglobin in response to hypoxia. This is a maladaptation to altitude and puts stress on the heart. Descent or phlebotomy may treat this.

Altitude Illness in Children
Altitude illnesses may occur in children as well as adults.

The following section is based on a consensus statement from the International Society for Mountain medicine in March 2001.
No large studies of children at altitude exist but several small studies show evidence of altitude illness in children.

The incidence of AMS may be the same for children as in adults. HAPE also occurs in children.

There are no published reports of HACE in children in the literature
At all ages altitude illness symptoms are non specific at first. In older children >8 years altitude illness is assumed to present as in adults.
Under 3 years, traveling children may be irritable and have differences in sleep, mood, appetite and activity from the travel alone.

In very young children altitude illness presents as fussiness, decreased appetite with possible vomiting, decreased playfulness and difficulty sleeping usually beginning 4-12 hrs after arriving at altitude.

A modified version of the Lake Louise Score for children helps look for problems.
Some children between ages 3-18 may have difficulty describing their symptoms making altitude illness even more difficult to recognize.

Prevention of altitude illness for children follows similar advice as for adults:
1. Graded ascent
2. Drug prophylaxis with acetazolamide 5mg/kg/day divided in 2-3 doses
3. Education- children and caregivers should be aware of altitude symptoms when traveling above 2500m
4. Emergency plan to descend and getting assistance should be made
5. Group Travel for over 2500m should be planned with:
a. Assessment of past medical history
b. Education of staff, children, parents on altitude
c. Wilderness first aid training
d. Emergency and evacuation planning

Treatment of altitude illness for children

AMS Mild Rest by stopping ascent or descend immediately till symptoms resolve.

Symptomatic treatment analgesics and antinausea medication
Moderate (worsening despite rest and above treatment)
Acetazolamide 2.5mg/kg/dose every 8 hrs-12 hrs (max 250mg per dose)
Dexamethasone 0.15mg/kg/dose every 6 hrs
Hyperbaric treatment only if descent delayed
Pain medication- Tylenol is recommended over aspirin because of possible Reye's Syndrome

Treatment of High Altitude Pulmonary Edema
for Children 
Sit upright
Nifedipine .5mg/kg/dose every 8 hrs Max 20mg tab or 40mg slow release
Consider Dexamethasome for concurrent HACE
Hyperbaric treatment only if descent delayed

Treatment  of High Altitude Cerebral Edema
for Children

Dexamethasone 0.15mg/kg/dose every 6 hrs
Hyperbaric treatment only if descent delayed


Advice for self assessment at altitude

When our travelers are having problems we suggest they read our pamphlet on high altitude on our website. There are lots of good resources on High Altitude on the website and we have presented a few.
The Lake Louise Questionnaire was designed to help people decide if they are having altitude illness.

Further comments on a modified application of the Lake Louise Score for children is covered at http://www.high-altitude-medicine.com/

For your reference a downloadable version of this text can be found at these links.
Front Page - Back Page

Other very good resources we suggest reviewing include

Himalayan rescue Association is based out of Kathmandu and is organized to fight altitude illnesses